1. Technical Field
The present invention relates to a method and apparatus for detecting regions in the tissue with the elasticity different from that of the surrounding tissues using a pressure sensing array for diagnosing breast cancer and other breast diseases accompanied by changes in the tissue elasticity.
2. Description of the Prior Art
Diagnosing early formation of tumors, particularly those caused by cancer, has been a problem that has been attempted to be solved using various techniques, such as ultrasonic imaging, nuclear magnetic resonance imaging, x-rays, and the like. Each of these techniques have limitations, including the application of radiation to the body, which may be harmful to the body being tested.
One of the safest and oldest techniques of detecting diseased tissue is palpation. Palpation, that is, examination using the sense of touch, is based on the significant differences in elasticity of normal tissues and certain lesions. Palpation has been a commonly used technique for detecting prostate and breast cancer. Surprisingly, over 90% of breast cancer is first detected by women themselves (Strax P., Control of breast cancer through mass screening, Hospimedica, March/April, pp. 35-40 (1989)), in spite of palpation being very subjective, not able to detect tumors of less than about 8 mm in diameter, and, besides, being capable of sensing lumps only when their elastic modulus is a few times higher than that for normal glandular tissue. Nevertheless, the manual palpation till now is one of the major methods of clinical examination of the breast just because of the great scale changes of mechanical properties of tissues in the course of development of cancer. Many tumors that are currently considered "nonpalpable" because of their small size or insufficiently high Young's modulus, nevertheless, can be detected mechanically if a more sensitive instrument than a finger could be used. Thus, development of a method that will enable physicians to obtain quantitative objective information on changes of elasticity of breast tissues with sensitivity and spatial resolution considerably higher than that of palpation would be a significant step in the early diagnostics of breast cancer.
Various types of devices mimicking palpation to detect tumors using different types of pressure sensors have been suggested. For example, Frei et al., U.S. Pat. No. 4,250,894, have proposed an instrument for breast examination that uses a plurality of spaced piezoelectric strips which are pressed into the body being examined by a pressure member which applies a given periodic or steady stress to the tissue beneath the strips. A different principle for evaluating the pattern of pressure distribution over a compressed breast was proposed by Gentle (Gentle CR, Mammobarography: a possible method of mass breast screening, J. Biomed. Eng. 10, 124-126, 1988). The pressure distribution is monitored optically by using the principle of frustrated total internal reflection to generate a brightness distribution. Using this technique, referred to as "mammobarography," simulated lumps in breast prostheses have been detected down to a diameter of 6 mm. According to Gentle, this technique can be used for mass breast screening; however, no quantitative data on lumps in a real breast was ever published. The failure has been explained by the insufficient sensitivity of the registration system. It should be noted, that most of the development of pressure sensors for medical applications has been done not for mimicking palpation but for monitoring blood pressure and analyzing propagation of pulse waves in blood vessels (See, for example, U.S. Pat. Nos. 4,423,738; 4,799,491; 4,802,488; 4,860,761).
Another approach to evaluate elasticity of the tissues uses indirect means, such as conventional imaging modalities (ultrasound or MRI) which are capable to detect motion of a tissue subjected to an external force. One approach attempts to determine the relative stiffness or elasticity of tissue by applying ultrasound imaging techniques while vibrating the tissue at low frequencies. See. e.g., K. J. Parker et al, U.S. Pat. No. 5,099,848; R. M. Lerner et al., Sono-Elasticity: Medical Elasticity Images Derived From Ultrasound Signals in Mechanically Vibrated Targets, Acoustical Imaging, Vol. 16, 317 (1988); T. A. Krouskop et al., A Pulsed Doppler Ultrasonic Svstem for Making Non-Invasive Measurement of Mechanical Properties of Soft Tissue, 24 J. Rehab. Res. Dev. Vol. 24, 1 (1987); Y. Yamakoshi et al., Ultrasonic Imaging of Internal Vibration of Soft Tissue Under Forced Vibration, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 7, No. 2, Page 45 (1990).
Another method proposed for measuring and imaging tissue elasticity is described in Ophir et al., U.S. Pat. Nos. 5,107,837, 5,293,870, 5,143,070 and 5,178,147. This method includes emitting ultrasonic waves along a path into the tissue and detecting an echo sequence resulting from the ultrasonic wave pulse. The tissue is then compressed (or alternatively decompressed from a compressed state) along the path and during such compression, a second pulse of ultrasonic waves are sent along the path into the tissue. The second echo sequence resulting from the second ultrasonic wave pulse is detected and then the differential displacement of selected echo segments of the first and second echo sequences are measured. A selected echo segment of the echo sequence, i.e., reflected RF signal, corresponds to a particular echo source within the tissue along the beam axis of the transducer. Time shifts in the echo segment are examined to measure compressibilities of the tissue regions.
Thus, since current prior art methods and devices for detecting lesions in breast by evaluating tissue elasticity are inferior to manual palpation, there still remains a need for a simple and effective device for the detection of breast cancer.